Atomic layer deposition has been proposed as an example of a film formation method. Atomic layer deposition, which is referred to as ALD, is a film formation process in which layers are deposited in a layer-by-layer manner at an atomic level by chemically reacting the substances which are adsorbed on the surface. A highly reactive gas, which is referred to as a precursor, and a reactive gas are alternately used to perform adsorption on the substrate surface and chemical reactions subsequent to the adsorption to thereby grow thin layers in a layer-by-layer manner at an atomic level. The reactive gas is also called a precursor in the ALD process.
Specifically, by using a self-limiting effect in surface adsorption that prohibits a certain type of gas from being adsorbed onto a surface after the surface is covered by the gas, only one layer of precursor is adsorbed onto the surface and unreacted precursor is purged. Then, the reactive gas is introduced to oxidize or reduce the above precursor to thereby obtain one thin layer having a desired composition. After that, the reactive gas is purged. This cycle is repeated so as to grow thin layers in a layer-by-layer manner. Accordingly, the thin layers grow in two dimensions in the ALD process. The ALD is characterized by having fewer defects in film formation, and is expected to be applied to various fields.
In the ALD process, a film formation apparatus and a film formation method of a time-divided type have been proposed, in which supply and discharge of precursors are repeatedly performed in a single chamber. The film formation apparatus and the film formation method of a time-divided type have a problem of a slow speed of film formation, since one layer is deposited in each cycle at an atomic level.
In order to solve the above problem, a space-divided type has been proposed, in which the chamber is divided into a several zones (areas) so that a single precursor or purge gas is supplied into the respective zones while the substrate is reciprocated among the zones (e.g., see PTL 1). The ALD process of a space-divided type significantly improves the speed of film formation.
In the space-divided type ALD process, a flexible substrate is typically transported along a predetermined transportation path in a chamber while being reciprocated among the zones. In the chamber, each zone has at least one supply port that supplies gas and one discharge port that discharges gas so that the gas is supplied and discharged to be distributed at a desired concentration.